diff --git a/lib/replace/replace.c b/lib/replace/replace.c
index 12716ea..0197b10 100644
--- a/lib/replace/replace.c
+++ b/lib/replace/replace.c
@@ -30,6 +30,7 @@
 #include "system/syslog.h"
 #include "system/locale.h"
 #include "system/wait.h"
+#include "../util/safe_string.h"
 
 #ifdef _WIN32
 #define mkdir(d,m) _mkdir(d)
@@ -466,7 +467,7 @@ char *rep_strcasestr(const char *haystack, const char *needle)
 	const char *s;
 	size_t nlen = strlen(needle);
 	for (s=haystack;*s;s++) {
-		if (toupper(*needle) == toupper(*s) &&
+		if (ascii_toupper(*needle) == ascii_toupper(*s) &&
 		    strncasecmp(s, needle, nlen) == 0) {
 			return (char *)((uintptr_t)s);
 		}
diff --git a/lib/util/charset/charcnv.c b/lib/util/charset/charcnv.c
index e9f6ab0..4e46cfc 100644
--- a/lib/util/charset/charcnv.c
+++ b/lib/util/charset/charcnv.c
@@ -135,21 +135,6 @@ static smb_iconv_t get_conv_handle(struct smb_iconv_convenience *ic,
 				   charset_t from, charset_t to)
 {
 	const char *n1, *n2;
-	static bool initialised;
-
-	if (initialised == false) {
-		initialised = true;
-		
-#ifdef LC_ALL
-		/* we set back the locale to C to get ASCII-compatible
-		   toupper/lower functions.  For now we do not need
-		   any other POSIX localisations anyway. When we
-		   should really need localized string functions one
-		   day we need to write our own ascii_tolower etc.
-		*/
-		setlocale(LC_ALL, "C");
-#endif
-	}
 
 	if (ic->conv_handles[from][to]) {
 		return ic->conv_handles[from][to];
diff --git a/lib/util/charset/codepoints.c b/lib/util/charset/codepoints.c
index 8be2051..95e7e77 100644
--- a/lib/util/charset/codepoints.c
+++ b/lib/util/charset/codepoints.c
@@ -21,6 +21,7 @@
 #include "includes.h"
 #include "system/locale.h"
 #include "dynconfig/dynconfig.h"
+#include "lib/util/safe_string.h"
 
 /**
  * @file
@@ -69,7 +70,7 @@ void load_case_tables(void)
 _PUBLIC_ codepoint_t toupper_m(codepoint_t val)
 {
 	if (val < 128) {
-		return toupper(val);
+		return ascii_toupper(val);
 	}
 	if (upcase_table == NULL) {
 		load_case_tables();
@@ -89,7 +90,7 @@ _PUBLIC_ codepoint_t toupper_m(codepoint_t val)
 _PUBLIC_ codepoint_t tolower_m(codepoint_t val)
 {
 	if (val < 128) {
-		return tolower(val);
+		return ascii_tolower(val);
 	}
 	if (lowcase_table == NULL) {
 		load_case_tables();
diff --git a/lib/util/charset/util_unistr.c b/lib/util/charset/util_unistr.c
index 520ce05..d445116 100644
--- a/lib/util/charset/util_unistr.c
+++ b/lib/util/charset/util_unistr.c
@@ -542,7 +542,7 @@ _PUBLIC_ void strlower_m(char *s)
 	   supported multi-byte character sets are ascii-compatible
 	   (ie. they match for the first 128 chars) */
 	while (*s && !(((uint8_t)*s) & 0x80)) {
-		*s = tolower((uint8_t)*s);
+		*s = ascii_tolower((uint8_t)*s);
 		s++;
 	}
 
@@ -581,7 +581,7 @@ _PUBLIC_ void strupper_m(char *s)
 	   supported multi-byte character sets are ascii-compatible
 	   (ie. they match for the first 128 chars) */
 	while (*s && !(((uint8_t)*s) & 0x80)) {
-		*s = toupper((uint8_t)*s);
+		*s = ascii_toupper((uint8_t)*s);
 		s++;
 	}
 
diff --git a/lib/util/safe_string.h b/lib/util/safe_string.h
index a6c052f..283a0ab 100644
--- a/lib/util/safe_string.h
+++ b/lib/util/safe_string.h
@@ -41,4 +41,7 @@
 
 #endif /* !_SPLINT_ */
 
+char ascii_tolower (char c);
+char ascii_toupper (char c);
+
 #endif
diff --git a/lib/util/util.c b/lib/util/util.c
index d645f7e..0582d35 100644
--- a/lib/util/util.c
+++ b/lib/util/util.c
@@ -602,12 +602,12 @@ _PUBLIC_ size_t strhex_to_str(char *p, size_t p_len, const char *strhex, size_t
 	}
 
 	for (; i < strhex_len && strhex[i] != 0; i++) {
-		if (!(p1 = strchr(hexchars, toupper((unsigned char)strhex[i]))))
+		if (!(p1 = strchr(hexchars, ascii_toupper((unsigned char)strhex[i]))))
 			break;
 
 		i++; /* next hex digit */
 
-		if (!(p2 = strchr(hexchars, toupper((unsigned char)strhex[i]))))
+		if (!(p2 = strchr(hexchars, ascii_toupper((unsigned char)strhex[i]))))
 			break;
 
 		/* get the two nybbles */
diff --git a/lib/util/util_str.c b/lib/util/util_str.c
index 0ea71a8..90dac6c 100644
--- a/lib/util/util_str.c
+++ b/lib/util/util_str.c
@@ -289,7 +289,7 @@ _PUBLIC_ int strwicmp(const char *psz1, const char *psz2)
 			psz1++;
 		while (isspace((int)*psz2))
 			psz2++;
-		if (toupper((unsigned char)*psz1) != toupper((unsigned char)*psz2) 
+		if (ascii_toupper((unsigned char)*psz1) != ascii_toupper((unsigned char)*psz2) 
 		    || *psz1 == '\0'
 		    || *psz2 == '\0')
 			break;
@@ -332,4 +332,22 @@ _PUBLIC_ void string_replace(char *s, char oldc, char newc)
 	}
 }
 
+/**
+ like tolower(), but only for ascii letters, to not depend on C locale
+**/
+char ascii_tolower (char c)
+{
+	if (c >= 'A' && c <= 'Z')
+		c = c + 32;
+	return c;
+}
 
+/**
+ like toupper(), but only for ascii letters, to not depend on C locale
+**/
+char ascii_toupper (char c)
+{
+	if (c >= 'a' && c <= 'z')
+		c = c - 32;
+	return c;
+}
diff --git a/source4/dsdb/common/util.c b/source4/dsdb/common/util.c
index b9bff91..c3e0538 100644
--- a/source4/dsdb/common/util.c
+++ b/source4/dsdb/common/util.c
@@ -42,6 +42,7 @@
 #include "dsdb/common/util.h"
 #include "lib/socket/socket.h"
 #include "dsdb/samdb/ldb_modules/util.h"
+#include "lib/util/safe_string.h"
 
 /*
   search the sam for the specified attributes in a specific domain, filter on
@@ -2815,10 +2816,10 @@ const char *samdb_cn_to_lDAPDisplayName(TALLOC_CTX *mem_ctx, const char *cn)
 	if (tokens == NULL)
 		return NULL;
 
-	/* "tolower()" and "toupper()" should also work properly on 0x00 */
-	tokens[0][0] = tolower(tokens[0][0]);
+	/* "ascii_tolower()" and "ascii_toupper()" should also work properly on 0x00 */
+	tokens[0][0] = ascii_tolower(tokens[0][0]);
 	for (i = 1; i < str_list_length((const char **)tokens); i++)
-		tokens[i][0] = toupper(tokens[i][0]);
+		tokens[i][0] = ascii_toupper(tokens[i][0]);
 
 	ret = talloc_strdup(mem_ctx, tokens[0]);
 	for (i = 1; i < str_list_length((const char **)tokens); i++)
diff --git a/source4/lib/ldb/common/attrib_handlers.c b/source4/lib/ldb/common/attrib_handlers.c
index 2f4454c..a929e41 100644
--- a/source4/lib/ldb/common/attrib_handlers.c
+++ b/source4/lib/ldb/common/attrib_handlers.c
@@ -29,6 +29,7 @@
 #include "ldb_private.h"
 #include "system/locale.h"
 #include "ldb_handlers.h"
+#include "lib/util/safe_string.h"
 
 /*
   default handler that just copies a ldb_val.
@@ -227,7 +228,7 @@ int ldb_comparison_fold(struct ldb_context *ldb, void *mem_ctx,
 		 * never appear in multibyte sequences */
 		if (((unsigned char)s1[0]) & 0x80) goto utf8str;
 		if (((unsigned char)s2[0]) & 0x80) goto utf8str;
-		if (toupper((unsigned char)*s1) != toupper((unsigned char)*s2))
+		if (ascii_toupper((unsigned char)*s1) != ascii_toupper((unsigned char)*s2))
 			break;
 		if (*s1 == ' ') {
 			while (n1 && s1[0] == s1[1]) { s1++; n1--; }
@@ -249,15 +250,15 @@ int ldb_comparison_fold(struct ldb_context *ldb, void *mem_ctx,
 		while (n2 && *s2 == ' ') { s2++; n2--; }		
 	}
 	if (n1 == 0 && n2 != 0) {
-		return -(int)toupper(*s2);
+		return -(int)ascii_toupper(*s2);
 	}
 	if (n2 == 0 && n1 != 0) {
-		return (int)toupper(*s1);
+		return (int)ascii_toupper(*s1);
 	}
 	if (n2 == 0 && n2 == 0) {
 		return 0;
 	}
-	return (int)toupper(*s1) - (int)toupper(*s2);
+	return (int)ascii_toupper(*s1) - (int)ascii_toupper(*s2);
 
 utf8str:
 	/* no need to recheck from the start, just from the first utf8 char found */
@@ -273,9 +274,9 @@ utf8str:
 		if (ret == 0) {
 			if (n1 == n2) return 0;
 			if (n1 > n2) {
-				return (int)toupper(s1[n2]);
+				return (int)ascii_toupper(s1[n2]);
 			} else {
-				return -(int)toupper(s2[n1]);
+				return -(int)ascii_toupper(s2[n1]);
 			}
 		}
 		return ret;
diff --git a/source4/lib/ldb/common/ldb_utf8.c b/source4/lib/ldb/common/ldb_utf8.c
index 73ae71b..cc98464 100644
--- a/source4/lib/ldb/common/ldb_utf8.c
+++ b/source4/lib/ldb/common/ldb_utf8.c
@@ -33,7 +33,7 @@
 
 #include "ldb_private.h"
 #include "system/locale.h"
-
+#include "lib/util/safe_string.h"
 
 /*
   this allow the user to pass in a caseless comparison
@@ -62,7 +62,7 @@ char *ldb_casefold_default(void *context, void *mem_ctx, const char *s, size_t n
 		return NULL;
 	}
 	for (i=0;ret[i];i++) {
-		ret[i] = toupper((unsigned char)ret[i]);
+		ret[i] = ascii_toupper((unsigned char)ret[i]);
 	}
 	return ret;
 }
@@ -118,7 +118,7 @@ char *ldb_attr_casefold(void *mem_ctx, const char *s)
 		return NULL;
 	}
 	for (i = 0; ret[i]; i++) {
-		ret[i] = toupper((unsigned char)ret[i]);
+		ret[i] = ascii_toupper((unsigned char)ret[i]);
 	}
 	return ret;
 }
diff --git a/source4/lib/samba3/smbpasswd.c b/source4/lib/samba3/smbpasswd.c
index 502f13f..1163748 100644
--- a/source4/lib/samba3/smbpasswd.c
+++ b/source4/lib/samba3/smbpasswd.c
@@ -55,6 +55,7 @@
 #include "includes.h"
 #include "system/locale.h"
 #include "lib/samba3/samba3.h"
+#include "lib/util/safe_string.h"
 
 /*! Convert 32 hex characters into a 16 byte array. */
 
@@ -70,8 +71,8 @@ struct samr_Password *smbpasswd_gethexpwd(TALLOC_CTX *mem_ctx, const char *p)
 	
 	for (i = 0; i < (sizeof(pwd->hash) * 2); i += 2)
 	{
-		hinybble = toupper(p[i]);
-		lonybble = toupper(p[i + 1]);
+		hinybble = ascii_toupper(p[i]);
+		lonybble = ascii_toupper(p[i + 1]);
 		
 		p1 = strchr_m(hexchars, hinybble);
 		p2 = strchr_m(hexchars, lonybble);
diff --git a/source4/ntvfs/posix/pvfs_shortname.c b/source4/ntvfs/posix/pvfs_shortname.c
index 530def9..ea2dd82 100644
--- a/source4/ntvfs/posix/pvfs_shortname.c
+++ b/source4/ntvfs/posix/pvfs_shortname.c
@@ -23,6 +23,7 @@
 #include "system/locale.h"
 #include "vfs_posix.h"
 #include "param/param.h"
+#include "lib/util/safe_string.h"
 
 /*
   this mangling scheme uses the following format
@@ -471,7 +472,7 @@ static char *name_map(struct pvfs_mangle_context *ctx,
 		if (! FLAG_CHECK(lead_chars[i], FLAG_ASCII)) {
 			lead_chars[i] = '_';
 		}
-		lead_chars[i] = toupper((unsigned char)lead_chars[i]);
+		lead_chars[i] = ascii_toupper((unsigned char)lead_chars[i]);
 	}
 	for (;i<ctx->mangle_prefix;i++) {
 		lead_chars[i] = '_';
@@ -491,7 +492,7 @@ static char *name_map(struct pvfs_mangle_context *ctx,
 		for (i=1; extension_length < 3 && dot_p[i]; i++) {
 			unsigned char c = dot_p[i];
 			if (FLAG_CHECK(c, FLAG_ASCII)) {
-				extension[extension_length++] = toupper(c);
+				extension[extension_length++] = ascii_toupper(c);
 			}
 		}
 	}
@@ -589,10 +590,10 @@ static void init_tables(struct pvfs_mangle_context *ctx)
 		ctx->char_flags[c2] |= FLAG_POSSIBLE2;
 		ctx->char_flags[c3] |= FLAG_POSSIBLE3;
 		ctx->char_flags[c4] |= FLAG_POSSIBLE4;
-		ctx->char_flags[tolower(c1)] |= FLAG_POSSIBLE1;
-		ctx->char_flags[tolower(c2)] |= FLAG_POSSIBLE2;
-		ctx->char_flags[tolower(c3)] |= FLAG_POSSIBLE3;
-		ctx->char_flags[tolower(c4)] |= FLAG_POSSIBLE4;
+		ctx->char_flags[ascii_tolower(c1)] |= FLAG_POSSIBLE1;
+		ctx->char_flags[ascii_tolower(c2)] |= FLAG_POSSIBLE2;
+		ctx->char_flags[ascii_tolower(c3)] |= FLAG_POSSIBLE3;
+		ctx->char_flags[ascii_tolower(c4)] |= FLAG_POSSIBLE4;
 
 		ctx->char_flags[(unsigned char)'.'] |= FLAG_POSSIBLE4;
 	}